1. Field of the Invention
The invention relates generally to catheters and methods of manufacture thereof which include the formation of a relatively soft tip onto a relatively rigid catheter body. More specifically, the invention relates to catheters useful for insertion into a living body for performance of medical procedures, such as angiography and guiding catheters for use in angioplasty procedures and other therapeutic and/or diagnostic procedures, and methods of manufacturing the catheter, specifically including methods of forming the soft tip thereon.
2. Brief Description of the Prior Art
It is common for many surgical procedures to include the insertion of a catheter into a living body. In some instances, such as during angiography or angioplasty procedures, it is common to insert a catheter long distances through vessels which are formed of fragile vascular or heart wall tissue which can be easily damaged or even pierced by the catheter during the insertion process if extreme care is not taken. Catheters used for such purposes must be sufficiently rigid to be advanced long distances through a vessel (by pushing from the proximal end thereof), and able to resist twisting or torque forces. Often, such catheters must be performable into a particular shape corresponding to a particular vessel pathway through which it must pass, and/or be able to withstand high fluid pressures during use.
Because these catheters are of necessity formed of a relatively rigid material, the distal tip thereof can be very destructive to the delicate vessel wall tissue through which the catheter passes. A catheter with a rigid distal tip can severely damage a vessel or heart wall, and although rare, may actually pierce through to the exterior of the tissue wall causing severe trauma to the patient or even death.
This problem has been addressed in the past by forming the distal end of the relatively rigid catheter with a relatively soft tip which is either non-traumatic or significantly less traumatic to vessel wall tissue than the relatively rigid material forming the body of the catheter. A catheter having a soft tip which is exemplary of the prior art is disclosed in U.S. Pat. No. 3,485,234 to Stevens, and U.S. Pat. No. 4,636,272 to Riggs.
Catheters have been formed in prior art manufacturing procedures by extruding catheter material over an elongated cylindrical core having a uniform diameter which ensures that the resultant catheter is formed to a uniform inner diameter. The catheter is then removed from the core or the core is stretched to reduce its diameter for purposes of later removal, and a distal end of the catheter is prepared to receive a relatively soft tip, either by chemical bonding such as adhesion, or by thermal bonding such as fusion of a soft tip material to the distal end of the catheter.
If fusion is used to join the soft tip to the catheter, a fusion rod may be inserted through the soft tip and the catheter, and heat is applied at the interface of the soft tip and the catheter distal end in order to fuse the materials together. Once cooled, the fusion rod and/or core is then removed and the soft tip is trimmed to the desired length.
It has been difficult to maintain a constant uniform internal and external diameter throughout the entire length of the catheter body/soft tip interface using the prior art processes of manufacture. Also, it has often been difficult to eliminate foreign material build up within the internal diameter of the catheter during the tip formation phase of the manufacturing process. Further, when heat is used to bond the materials together at the catheter body/soft tip interface, it has often been necessary to insert a fusion rod into the already formed catheter and soft tip in order to help maintain the desired internal diameter during the fusion and cooling processes.
There therefore exists a need in the art to develop a relatively rigid catheter having a relatively soft tip which is formed of a uniform internal diameter across the catheter body/soft tip interface. There is further a need in the art to develop a manufacturing process which includes heat fusion of a soft tip to a relatively rigid catheter body, which eliminates the need for a special fusion rod to be inserted through the catheter and soft tip thereof as part of the fusion process.